1. (Field of the Invention)
The present invention relates to photopolymerizable compositions which can be cured by using active energy rays and transparent cured products obtained by irradiating the above compositions with active energy rays and, particularly, plastic lenses that can be produced within short periods of time exhibiting little optical distortion, excellent transparency, surface precision, impact resistance and tinting property, and are suited for spectacles.
2. (Description of the Prior Art)
Owing to their light weight, impact resistance and tinting property, the glass lenses for spectacles have now been replaced by plastic lenses. A typical plastic lens may be a polymer, i.e., diethylene glycol bisallylcarbonate (CR-39) having a refractive index of as small as about 1.50. In the case of a minus lens having a high power, therefore, the thickness at the edges become so large that the merit of reduced weight which is a feature of a plastic is lost.
In molding the plastic lenses, in general, a polymerizable monomer is poured into between two pieces of glass molds having different radii of curvature, and the lenses are molded based upon the heat polymerization only. According to the method based on the heat polymerization only, however, the polymerization time is usually as long as several hours, which is not satisfactory from the standpoint of productivity of the molded articles.
A method of molding plastic lenses within short periods of time by irradiating a radical polymerizable monomer with active energy rays been disclosed in Japanese Laid-Open Patent Publication No. 166305/1985, and it has been desired to obtain a resin having a high refractive index that can be molded within short periods of time upon irradiation with active energy rays.
When a plastic lens is molded within a short period of time upon irradiation with active energy rays in accordance with the method disclosed in the above publication, however, an internal stress is built up due to the contraction by polymerization, and the central portion of the lens after annealing is deformed due to the internal stress, and the shape of surface of the mold that is used is not correctly transferred.
As a method of decreasing contraction due to polymerization, Japanese Laid-Open Patent Publication No. 254655/1989 discloses a method of photopolymerizing a thioetheracrylate oligomer. However, the above oligomer is poorly compatible with other acrylate monomers or methacrylate monomers, and causes the mixture of the oligomer and these monomers to become into haze when the oligomer is copolymerized with these monomers. That is, in producing the plastic lenses, several kinds of monomers have usually been copolymerized in order to improve lens properties such as heat resistance, hardness, etc. When the oligomer is used, however, strict limitation is imposed on the kind of the monomer that is to be copolymerized.
Japanese Laid-Open Patent Publications Nos. 11613/1992 and 11618/1992 disclose di(meth)acrylate polymerizable compounds having, in the molecules thereof, two ester groups excluding esters due to (meth)acrylate. These compounds, however, exhibit large contraction factors when being cured, and the surfaces of the mold are not correctly transferred to the cured product. Besides, these compounds have poor impact resistance. Moreover, these compounds exhibit poor compatibility to other ethylenically unsaturated monomers. When the mixtures of these compounds and other ethylenically unsaturated monomers are cured, therefore, the cured products are so distorted that the cured products peel off from the mold in many case.